Method for Tunnel Construction

ABSTRACT

There is provided a method of constructing a section of a half-tunnel in a slope ( 10 ) of a mountain or hill ( 12 ), including the steps of forming a lock block ( 18 ) along the section ( 16 ) above the upper edge of the half-tunnel to be excavated, inserting lock elements ( 22 ) traversing the lock block and extending into the mountain, excavating portions of the mountain beyond and below the lock block defining roof and bottom portions of the half-tunnel, and repeating the excavating procedure until the entire section of the half-tunnel is formed.

FIELD OF THE INVENTION

The present invention relates to the construction of tunnels, and more particularly, to a method of constructing or widening a half-tunnel in a ground typically in a hillside or mountainside.

BACKGROUND OF THE INVENTION

The building or widening of roads along mountains or hill sides presents major problems, inter alia, with respect to damage caused to the environment including forests, and may cause instability and landslides, as is well known and understood by men skilled in the art. With a view to overcome the problems, the construction of half tunnels was developed, however, so far has not provided an optimal solution, at least from the practical aspect of the necessity to support the roof of such a half tunnel. As illustrated in FIG. 1, when a regular tunnel 2 is constructed, two opposing compression forces indicated by arrows F, F₁ are developed in the roof of the tunnel, which forces achieve equilibrium. Thus, depending on the type of ground in which the tunnel is excavated, reinforcing soil nails 6 may sometimes be required to be inserted into the ground. When such nails 6 are utilized, they are inserted into the ground as shown, radially with respect to the arched tunnel roof. Hence, since a half-tunnel does not have a center opposing force in its roof, the above-described method of tunnel construction is not applicable. The obvious solution used is to provide a support to the free edge of the roof in the form of struts or posts extending between the base of the tunnel, e.g., the road and the roof. The disadvantages of such supporting posts are readily apparent.

SUMMARY OF THE INVENTION

It is therefore a broad object of the present invention to overcome the disadvantages of the prior art half-tunnel construction and to provide a method for constructing a half-tunnel, which does not include supporting posts at the open side of the tunnel.

It is a further object of the present invention to provide a method for constructing a half-tunnel, the roof of which is securely supported by lock elements inserted into the ground above the roof.

In accordance with the present invention there is therefore provided a method of constructing a section of a half-tunnel in a slope of a mountain or hill, comprising the steps of: a) forming a lock block along said section above the upper edge of the half-tunnel to be excavated; b) inserting lock elements traversing said lock block and extending into said mountain; c) excavating portions of the mountain beyond and below said lock block defining roof and bottom portions of said half-tunnel, and d) repeating step c) until the entire section of said half-tunnel is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings:

FIG. 1 (prior art) is a schematic representation of a regular tunnel construction;

FIG. 2 is a schematic cross-sectional view of a first stage of the method of a half-tunnel construction, according to the present invention;

FIG. 3 is a schematic, cross-sectional view of a second stage of the method of a half-tunnel construction, according to the present invention;

FIG. 4 is a schematic, cross-sectional view of a third stage of the method of a half-tunnel construction, according to the present invention, and

FIG. 5 is schematic, cross-sectional view of a fourth stage of the method of a half-tunnel construction, according to the present invention, having additional protection against falling rocks.

DETAILED DESCRIPTION

The method of constructing a section of a tunnel in a slope of a mountain or hill according to the present invention will now be described with reference to the construction stages. The first stage is illustrated in FIG. 2, showing a slope 10 of a hill or mountain 12. After determining the height h from a level 14, e.g., a road of the tunnel section to be constructed, a small recess 16, e.g., an L-shaped recess is formed, and a lock block 18 is placed on the base 20 of the recess 16. The lock block 18 is advantageously a prismatic body, e.g., a prefabricated steel reinforced concrete slab. Alternatively, such steel reinforced concrete lock blocks can be casted in-situ. Lock elements 22, which are typically heavy duty soil nails or pre-stressed anchors, are then driven or drilled into the slope of the hill or mountain 12 through the lock block 18. The lock elements 22 are of substantial length, intended to extend sufficiently above the width of the tunnel to be dug for providing support. Also, as seen in the Figure, the lock elements fan out at different angles with respect to the plane of the lock block 18, from an angle slightly less than the general angle of the slope 10 to an angle slightly greater than 90°. These lock elements 22 provide the required compression forces necessary to balance the half-tunnel to be excavated in order to achieve the equilibrium, which compression forces are normally provided by the “opposing half-tunnels” when a regular tunnel is constructed, as shown in FIG. 1.

When the ground of the slope 10 of a hill or mountain 12 in which the half-tunnel is to be formed is composed of unstable material such as crushed or weathered stones, fill-in soil or the like, it is recommended to first stabilize the ground by known techniques, such as injection of hardenable chemicals or any soil reinforcement materials, or still otherwise, by driving in anchors or soil nails in a grid-like pattern.

Once the ground above the planned half-tunnel is secured by the lock block 18 and lock elements 22, excavation of the half-tunnel from top to bottom as indicated by the arrow E, can commence, as illustrated in FIG. 3. When a roof portion 24 is formed, depending on the ground type, soil nails 26 traversing the directions of the lock elements 22, may be added, to form a reinforcing grid above the half-tunnel. Shot crete 28 may be applied to the roof before or after the insertion of the soil nails 26. This excavation process and subsequent insertion of soil nail 26 while covering the half-tunnel roof with shot crete is repeated until the entire half-tunnel is excavated and formed, as seen in FIG. 4. The shot crete 28 can then be covered by a suitable facing providing greater strength to the roof of the half-tunnel.

Referring to FIG. 5, there is seen a half-tunnel constituting an expanded road 30 formed in the slope 10 of a mountain 12. In cases where a danger of falling rocks or sliding soil exists, a visor-like projection 32 may be attached to the front of the lock block 18, which protection 32 may take different forms. It may be configured to direct falling rocks to continue their movement beyond the road 30 into the other part 34 of the slope 10, and/or be configured as a trough, which is capable of retaining sliding and falling soil and rocks.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 

1. A method of constructing a section of a half-tunnel in a slope of a mountain or hill, comprising the steps of: a) forming a lock block along said section above the upper edge of the half-tunnel to be excavated; b) inserting lock elements traversing said lock block and extending into said mountain; c) excavating portions of the mountain beyond and below said lock block defining roof and bottom portions of said half-tunnel, and d) repeating step c) until the entire section of said half-tunnel is formed.
 2. The method as claimed in claim 1, further comprising the step of forming a recess in the slope above the upper edge of the half-tunnel to be excavated.
 3. The method as claimed in claim 1, further comprising inserting soil nails in the roof portion extending in directions substantially normal to the roof of the half-tunnel.
 4. The method as claimed in claim 1, further comprising the step of applying shot crete to the roof portion after step c).
 5. The method as claimed in claim 1, further comprising the step of applying a shot crete to the roof of the entire half-tunnel section after step d).
 6. The method as claimed in claim 1, further comprising the step of injecting hardenable chemicals or any soil reinforcement materials, or driving in anchors or soil nails in a grid-like pattern, prior to, or after step a).
 7. The method as claimed in claim 1, further comprising the step of applying a facing to the roof of the half-tunnel.
 8. The method as claimed in claim 1, further comprising attaching a projection to the exposed face of the lock block protecting against falling soil and rock. 